This invention relates to a filtration device and particularly to one adapted for use in the fuel supply circuit of a motor vehicle.
Motor vehicles such as diesel powered heavy duty trucks typically have a fuel supply system in which fuel is drawn from one or more tanks by a transfer pump and is then sent to the fuel injection pump of the engine. Since fuel injection pumps are very sensitive to contaminants such as water and large particulates, it is necessary to filter the fuel before it is transmitted to the injection pump. In many applications, a pair of particulate filters in series are used. A first filter, referred to in the industry as a "primary filter", filters the fuel flowing between the fuel tank and the transfer pump (fuel pump) as a means of protecting the transfer pump. Since transfer pumps are typically positive displacement types, large particulates can cause damage or premature wear of the pump. Complete failure of the pump could cause the motor vehicle to stop running. After the transfer pump, the fuel is again filtered before flowing to the fuel injection pump. For operation in cold weather conditions and as a means of separating water from the fuel, a fuel heating and/or a water separating device is often provided to treat the fuel before it is sent to the fuel injection pump. Such devices can be placed in the fuel circuit before the transfer pump (vacuum side) or after the transfer pump (pressure side). The assignee of this invention, the Davco Manufacturing Corporation, owns a number of patents relating to devices which perform both the fuel heating and water separating functions in one unit, including U.S. Pat. Nos. 4,368,716, 4,428,351, 4,395,996, 4,421,090, 4,495,069, 4,539,109, 4,680,110, 4,579,653, as well as a number of patent applications currently pending. Many of the devices described in these patents further incorporate particulate filters, thus providing fuel that is warm, clean and substantially water free.
Although dual filtration systems as described previously generally perform adequately, they have several significant drawbacks. Since the primary filter typically has a removable and disposable filter element, it must be serviced frequently and replaced with a new filter, thus contributing to maintenance costs. In addition, in cold weather operating conditions where fuel clouding and waxing can occur, the filter media element of the primary filter can become completely coated with wax deposits, thus creating a flow restriction which can starve the engine. Furthermore, free water often present in fuel which may collect in the primary filter cannot be conveniently drained and is therefore subject to freezing, and can contaminate the filter element.
This invention is directed to a primary filter which does not require the use of a replaceable filter element, thus minimizing maintenance requirements. This invention recognizes that the filtration requirements for protection of the transfer pump are less stringent than that for the fuel injection pump where extremely minute particulates and water can cause serious damage. The primary filter according to this invention also incorporates a means for removing trapped water and heavy particulates which precipitate out of the fuel and collect in the lower portion of the filter due to their relatively higher density. Such a feature is particularly advantageous where a water separator unit is used on the pressure side of the fuel delivery system. Water separation on the pressure side of the system tends to be more difficult. Water removed by the primary filter reduces water removal requirements of the downstream water separator. As additional refinements, the primary filter according to this invention may also incorporate a magnetic probe which attracts and retains magnetic particles suspended within the fuel. In addition, a relatively coarse particulate filter can be provided which preferably includes a bypass feature to allow wax deposits to pass through the filter which might be present in cold weather operating conditions. Wax flowing through the filter can be reduced downstream through the agitation and shearing action of the transfer pump and through heat applied by a fuel heating device (if provided). The filtration operation of the filter is provided by decreasing the velocity of the fuel to allow particulates and water to settle out, and also by causing the fuel to undergo an abrupt change in direction which also aids in separating out particulates and relatively high density contaminants such as water.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subject description of the preferred embodiments and the appended claims, taken in conjunction with the accompanying drawings.